Iraqi twin brothers have been remanded in custody in Finland on Friday for their alleged involvement in an Islamic State group massacre of Iraqi air force cadets last year.

The 23-year-olds, who have not been named, were placed in custody for four months at Pirkanmaa District Court in Tampere over the deaths of 11 unarmed young cadets in Tikrit last June.
The session was closed to the public.

In July 2015, IS released footage of the Tikrit massacre, in which its fighters executed hundreds of mostly Shia military recruits captured at the Speicher military base.

The highest estimates put the number of executed cadets at 1,700.
Finnish National Bureau of Investigation (NBI) chief inspector Jari Raty told the AFP news that the IS video was a central piece of evidence in the investigation.

"The nature of the crime is visible in the video... they (the suspects) were not hooded," he said.
Raty told Finnish public broadcaster YLE earlier that "the victims were lying on the ground and they were shot one by one".

He would not comment on why the Iraqi brothers had come to Finland in September, but Finnish media reported they had been staying at a reception centre for asylum seekers in the southwestern town of Forssa where they were arrested on Tuesday.

Other asylum seekers at the centre told tabloid Ilta-Sanomat they had sensed something "odd" about the twins' behaviour.

"I saw them sit alone and they would not talk to anyone. I knew they were hiding something," a 38-year-old asylum seeker and lawyer who gave his name as Omar Mohamedi told the paper.

Finland's Interior Minister Petteri Orpo reiterated an earlier estimate by the country's Security Police that around 300 people in the country are known to have connections to "terrorist" elements abroad.

The NBI said the arrests were the result of close co-operation between the national and local police forces who have been conducting asylum interviews with newly arrived refugees.

"The crucial intelligence has come from within the country but we do seek to co-operate with foreign authorities on this case," Raty said, refusing to confirm whether police had been tipped off by an asylum seeker.

The brothers were to appear behind closed doors at the Tampere district court in western Finland.

In July, 24 men were sentenced to death by an Iraqi court over their involvement in the massacre at Camp Speicher, used by US forces during the occupation and named after a US Navy pilot killed in action during the 1991 Gulf War.